Agent Skills: realitykit-rendering-materials

Implement and debug RealityKit rendering, materials, lighting, cameras, visual effects, post-processing, render cost controls, Gaussian splats, decals, lightmaps, probes, LOD, and occlusion on visionOS 27. Use when a RealityKit task is primarily about visual appearance, mesh/material display, lights, shadows, tone mapping, bloom, camera projection, rendering performance, or choosing rendering components instead of animation, audio, interaction, or custom ECS behavior.